A source measure unit (SMU) can be programmed to power a developing device or a device under test. A conventional source measure unit can also monitor the voltage or current consumption of the developing device or device under test, and according to the voltage value or current value monitored, make an adjustment for the voltage or current to be supplied from the source measure unit. Therefore, the supplied voltage or current may fit the requirements of development or test, and the possibility of burning out the device may also decrease.
However, a conventional source measure unit usually adjusts the voltage or current to be supplied when it is monitored that the output voltage or current arrives a preset threshold; and this easily cause overshoot occurring to the supplied voltage or current. Moreover, when a conventional source measure unit switches its control loop, the output signal may have a disharmonious variation waveform, leading to the decrease of the reliability of power supply.